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Method And Apparatus For Reducing The Formation Of Spots In Laser Projection - Patent 6426836


This invention relates to a system for improving the image brightness and image sharpness in laser television projection systems.Laser projection uses a raster procedure to produce images. In the raster procedure, three primary colors red, green, and blue are emitted from one laser or from two or more different lasers. The three colors are modulated separately, broughttogether again, and scanned over a surface. The image is then formed by points, as in the standard television picture tube. The color of an image point is defined by the relative power of its primary color components. Normally the beam is deflectedhorizontally by a polygonal mirror and vertically by a galvanometric scanner.The laser beam causes image irregularities (spots) or so-called speckles in the laser image projection due to the spatial coherence of the laser light. The effect can be observed by shining a diverged laser beam onto a wall. The eye of a viewersees a disk with a stochastic light-dark distribution, instead of a uniformly illuminated field.The spots are perceived when light is reflected off a projection surface and to the eye. The projection surface has areas which are uneven compared with the size of the light source wavelength. The light waves reflected off these uneven surfaceareas of the projection surface reach the eye with different phase positions creating interference that is perceived in the eye. From a given standpoint of the observer, this interference produces a spatial two-dimensional light-dark pattern.A laser projection system is described in European Patent No. EP0589179A1 where laser radiation consisting of three primary colors is passed through a diffusion element in a common optical path. The diffusion element rotates in the range from 30to 40 rpm to prevent the formation of spots due to interference phenomena and creates a clearer, truer-color image.A projection light image display system with reduced spot formation is also described in European Patent No

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